1. Field of The Invention
The present invention relates to a method of polishing the chamfered portion of a semiconductor silicon substrate.
2. Description of Prior Art
When a thin film is formed on the surface of a semiconductor silicon substrate by epitaxial growth, before carrying out the epitaxial growth procedure, an oxidized silicon layer 1a is formed on the bottom surface of the above silicon substrate 1 by a method such as atmosphere CVD and so on, as shown in FIG. 6(a), to prevent the auto-doping of re-diffusing impurities within the substrate into the above growing layer. The oxidized silicon layer 1a covers not only a flat portion of the bottom surface of the semiconductor silicon substrate but also the chamfered portion around its circumference. Nodules are generated in epitaxial growth while the oxidized silicon layer 1a is formed on the above chamfered portion. The nodule is an abnormal product of epitaxial growth due to the shape of circumferential portion and the surface grain of the semiconductor silicon substrate 1. The nodules cause particle defects while the device is being formed. Therefore, edge relief is necessary to remove the oxidized silicon layer covering on the above chamfered portion. Referring to FIG. 6(b), the edge relief should adhere a protecting tape 5, which is slightly smaller than the shape of the bottom surface of the semiconductor silicon substrate 1, to the oxidized silicon layer 1a of the semiconductor silicon substrate 1 to protect the oxidized silicon layer 1a and to expose the circumferential portion. Thereafter, as shown in FIG. 6(c) the semiconductor silicon substrate 1 is cleaned by etching liquid such as fluoroacid and so on to remove the circumferential portion of the oxidized silicon layer. Furthermore, when the extrinsic gettering polysilicon layer and the oxidized silicon layer are formed on the bottom surface of the semiconductor silicon substrate to remove the impurity, the polysilicon layer and the oxidized silicon layer on the circumferential portion of the semiconductor silicon substrate must also be removed. Next, the protecting tape 5 is detached, on the chamfered portion a mirror polish is performed, and the semiconductor silicon substrate is cleaned.
Recently, demand for the mirror polishing of the chamfered portion of a semiconductor silicon substrate has increased. However, for the semiconductor silicon substrate having an oxidized silicon layer formed on the bottom thereof, the edge relief and the mirror polishing of the chamfered portion after CVD have to be carried out separately. Thus, two kinds of apparatus are required, and the working procedures are increased. The protecting tape being attached on the semiconductor silicon substrate while in edge relief has to be littered, which increases costs. Moreover, the cleaning has to be performed twice due to the edge relief and the mirror polish
Colloidal silica is used as polishing agent for lapping the chamfered portion of the semiconductor silicon substrate. However, it is difficult to remove the oxidized silicon layer formed on the semiconductor silicon substrate by colloidal silica. FIG. 7 illustrates the degree of polishing amount generated by carrying out the polishing of the oxidized silicon layer of the semiconductor silicon substrate (SiO.sub.2 part) and the portion exclusive of the oxidized silicon layer (Si portion) with colloidal silicon during a certain period of time. The variation of polishing amount for the Si portion (A in the drawing) depends on the variation of polish liquid pH value which demonstrates an effect of the combination of the chemical polishing and mechanical polishing,however the polishing amount of the SiO.sub.2 part (B in the drawing)is less than half that of the Si part, which is constant regardless of the pH variation. Accordingly, chemical polishing of the oxidized silicon layer cannot be expected to be effective, and polishing can only be achieved by the mechanical procedure. The oxidized silicon layer can be easily removed if SiC is used as abrasive grain, but the surface of the semiconductor silicon substrate roughs and a mirror polish cannot be obtained.